Ladders have long been used throughout the world for a variety of purposes. Fixed, single-section ladders may be conveniently used where the top of the ladder can be stabilized against a wall or other structure. Where no stabilizing structure is conveniently available, it is often desirable to use a stepladder having a ladder section and a prop section, the tops of these sections being hinged together so that they can be spread apart to form an inherently stable stepladder.
The desirable height of a ladder or stepladder depends on how high the object or space sought to be accessed is above the ground or working surface. For example, a 6-foot high ladder or stepladder may be satisfactory for gaining access as high as 10 feet or so above ground, but a considerably taller ladder would be needed if access must be had 20 feet above ground. However, such a taller ladder will not necessarily be suitable for convenient access to locations closer to the ground. If a particular project requires access to locations at a variety of heights, one option is to have available two or more ladders or stepladders of varying heights. This is not a preferred option, as it entails the extra expense of multiple ladders, the need to transport multiple ladders to and from the project site, and the need for an increased amount of space to store the ladders when they are not being used.
To address these problems, a number of adjustable ladders and stepladders have been developed over the years. There are numerous examples of extension ladders in the prior art, typically featuring an upper ladder section overlapping a lower ladder section. The two sections may slide relative to each other to create a ladder of a desired height, up to nearly double the height of a single section. By providing utility over a larger range of heights, and being collapsible for compact storage, extension ladders of this type have enjoyed widespread acceptance as a solution to the noted problems.
However, the mechanisms of conventional extension ladders typically work only for ladders having parallel rails. It is well known that a given structure, having a given top width, will have greater lateral stability if its base width is greater than at its top width, as compared to the case where the width is constant. This principle has often been applied to fixed ladders, especially tall ladders; i.e., it is well known to construct fixed ladders with flared rails, in order to enhance the ladders' lateral stability and therefore the safety of persons using the ladders. However, attempts to create an extension ladder having flared rails have not been successful.
The prior art discloses numerous examples of adjustable stepladders. U.S. Pat. No. 534,463, issued Feb. 19, 1895 to Bowser, U.S. Pat. No. 1,670,653, issued May 22, 1928 to Cummins, and U.S. Pat. No. 5,000,289, issued Mar. 19, 1991 to Sanchez, all disclose a stepladder featuring an upper ladder section and a slidable lower ladder section, plus an upper prop section and a slidable lower prop section. A disadvantage common to all of these inventions is that each requires one or both of the ladder sections to have parallel rails; i.e., they will not work where both the upper ladder section and the lower ladder section have the desirable feature of flared rails. Furthermore, in each of these inventions, the width of the upper ladder section must be controlled within close tolerances to suit the configuration of the lower ladder section.
For the foregoing reasons, there is a need for a stepladder which is conveniently adjustable in height when the rails of the ladder sections are flared as well as when they are parallel, and wherein the ladder section can be adjusted independently of the prop section. In addition, there is a need for an extension ladder which is conveniently adjustable in height when the rails of the ladder sections are flared, as well as when they are parallel. The present invention is directed to these needs.